Site characterization for engineering purposes using geophysical and geotechnical techniques

Geophysical and geotechnical techniques were applied to determine the suitability of the sub-surface structure of Akole community area, Abeokuta, Nigeria, for the construction of engineering structures (CES). Four vertical electrical soundings (VES) were carried out, and 10 samples from different points at 1 m depth were analysed to determine soil moisture content, specific gravity (SG), Atterberg limits and California bearing ratio (CBR). The geoelectric sections revealed a maximum of five layers with the typical sounding curves of AKH and HKH types. Sieve analysis and tests for compaction limit, Atterberg limits, SG, optimum moisture content and maximum dry density for compaction limit revealed that samples SP2, SP3, SP4, SP6, SP7, SP8, SP9 and SP10 are of low plasticity with SG values that fall within the permissible range, while SP1 and SP5 are of medium plasticity and their SG values fall below the range of standard specifications. CBR analysis showed that SP1 and SP5 have low load-bearing capacities. VES 1 and 2, linked with SP1 and SP5, are considered unstable and unsuitable to support the CES with shallow foundations; however, excavation of weak layers up to a depth of 5 m and reinforcement will enable the support.